In recent years, head mount display apparatuses, namely a HMD (Head Mount Display) used for watching contents images, such as movies and video, and remote control of industrial apparatuses and medical apparatuses have been developed.
In general, a HMD includes an eyepiece optical system for guiding an image obtained by the display element, such as a liquid crystal display and an organic EL, to the eyeball/eyeballs of a wearer of the HMD. The HMD allows the wearer of the HMD to watch a virtual image as if the image is magnified and displayed in the air by directly projecting the image obtained by the display element onto the eyeball/eyeballs of the wearer of the HMD.
For example, Japanese Patent Publication TOKKAI No. 2002-156600 discloses the technology of HMD including an eyepiece optical system configured by an optical substrate, onto the slant surface of the one end of which a hologram element is adhered as a reflective film for superimposing the image onto the front sight to display the image obtained by the display element, and a transparent plate shaped substrate, which supports the eyepiece optical system in the vicinity of the eyeball such as to face the eyeball. The structure of the eyepiece optical system and the support substrate disclosed in Japanese Patent Publication TOKKAI No. 2002-156600 will be briefly described by referring to FIG. 6(a) hereinafter. FIG. 6(a) illustrates a perspective view of the eyepiece optical system viewed obliquely from the right rear. FIG. 6(b) illustrates the support substrate viewed obliquely from the right rear. In the present specification, when wearing the HDM, the direction to the place where the eyeball is present, namely the direction toward the eyeball, is referred to as a back direction (an eyepiece direction) and the direction to the place where the image can be observed is referred to as a front direction.
As shown in FIG. 6(a), an eyepiece optical system 75 includes a prism 751, which is an optical substrate and a hologram element 752 (hereinafter, referred to as HOE (Holographic Optical Element)).
The surface on the lower side and the both side surfaces of the outer shape of the prism 751 are formed as the joint surfaces to be joined with the recessed cutout of the support substrate 5 when engaged with the recessed cutout, which will be described later. A slant surface 751a, onto which the HOE 752 is adhered, is formed to be the joint surface on the lower side of the prism 751. This slant surface 751a is formed such that the slant surface 751a has an inclination angle, which can guide a hologram image to the eyeball, when wearing the HMD. Further, the joint surfaces being the left and right side surfaces of the prism 751, are respectively formed to be slant surfaces 751c and 751d. The slant surface 751a slants upward from the edge thereof adjacent to the back surface (in the eyepiece direction) of the prism 751 toward the edge thereof adjacent to the front surface of the prim 751 (in the front direction). The slant surfaces 751c and 751d are located at a position off the optical axis L and are inclined with respect to the optical axis L, wherein the direction of inclination of the slant surfaces 751c and 751d are oriented such that the edges of the slant surfaces 751c and 751d adjacent to the front surface of the prism 751 are closer to the axis L than the edges of the slant surfaces 751c and 751d adjacent to the back surface of the prism 751. As described above, the slant surfaces 751a, 751c and 751d slant such that the outer shape of the prism 751 perpendicular to the axis L is smaller, as the outer shape is farther from the back surface and closer to the front surface of the prism 751.
Next, as illustrated in FIG. 6(b), a recessed cutout corresponding to the joint surfaces of the outer shape of the prism 751 is provided in the center portion of the support substrate 5. The recessed cutout is structured by slant surfaces 5a, 5c and 5d such as to respectively join with the slant surfaces 751a, 751c and 751d of the prism 751. As described above, the shape of the recessed cutout of the support substrate 5 is shaped corresponding to the outer shape of the prism 751.
The outer shape of the prism 751 is adhered to the support substrate 5 at the corresponding surfaces by adhesive agent, as described above, and integrated.
There have been studied various types of HMD having an eyepiece optical system and support substrate for supporting the eyepiece optical system such that the eyepiece optical system faces an eyeball, with a structure for guiding a image obtained from a display element such as a liquid crystal display or an organic EL to the eyeball of the wearer of the HMD and displaying it.
Since an eyepiece optical system is placed in the vicinity of an eyeball of the wearer of a HMD and is used facing the eyeball, the safety of the eyepiece optical system has to be secured. However, in the HMD disclosed in Japanese Patent Publication TOKKAI No. 2002-156600, three joint surfaces (slant surfaces 751a, 751c and 751d of the prism 751 and slant surfaces 5a, 5c, and 5c of the support substrate 5), by which the prism 751 joins with the support substrate 5, slant such that the outer shape of the prism perpendicular to the optical axis is smaller, as the outer shape is farther from the back surface and closer to the front surface of the prism 751. Namely, the outer shape of the prism 751 is formed in a trapezoid having a back surface as a bottom surface of the trapezoid. With this structure, it is difficult to stably place and join the prism 751 with the support substrate 5. Accordingly, when an impact is applied to the HMD, there is a possibility that the prism 751 is peeled off or drop off from the support substrate 5. Accordingly, it is necessary to consider the safety of the wearer of the HMD. However, the description about the improvement of the adhesive strength of the prism 751 to the support substrate 5 and the description about the attention to the safety of the HMD for the wearer of the HMD, are not disclosed nor suggested in Japanese Patent Publication TOKKAI No. 2002-156600.
To solve problems, as described above, an object of the present invention is to provide a durable head mount display apparatus having an eyepiece optical system and a support substrate for supporting the eyepiece optical system in the vicinity of an eyeball of a wearer who wears the head mount display apparatus such that the eyepiece optical system faces the eyeball of the wearer, wherein the eyepiece optical system is prevented from dropping from the support substrate and the head mount display apparatus is excellent in durability.